In U.S. Pat. No. 3,992,161 ('161) ODS iron-chromium alloys are described as having very good oxidation resistance coupled with high-strength at elevated temperatures. The results set forth therein reflect a decided improvement over iron-chromium alloys produced by the more conventional melt/ingot processing practices. More specifically, it was disclosed that the ODS alloys could be produced by the now well known Mechanical Alloying process, a technology developed nearly twenty years ago and described in such U.S. Pat. Nos. as 3,591,362 and 3,837,930.
Notwithstanding the virtues of the '161 alloys such materials have been found wanting in certain aerospace and industrial environments. By way of explanation, though the '161 ODS material (commercially contains about 20% chromium, 4.5% aluminum) exhibits good corrosion and oxidation resistance at, say, up to 1200.degree. C., it is prone to undergo premature slagging attack (formation of low melting point phases/compounds through a chemical reaction with corrosive deposits from and/or the environment per se) and/or accelerated attack upon exposure at higher temperatures after short intervals of time, the failure being of the catastrophic type. In this connection, accelerated oxidation may be considered as the rapid mass change of an alloy by oxidation. The mass change is virtually always dramatically positive if all the oxide is collected and weighed. In undergoing the ravages occasioned by such attack the alloy surface converts to friable iron oxide and iron-chromium spinels.
For example, burner cans in aircraft gas turbine engines of advanced design are currently intended for use at increasingly higher operating temperatures, i.e., about 1250.degree. C. (2308.degree. F.), and above, e.g., 1300.degree. C. (2372.degree. F.). Similarly, industrial applications involving intimate contact with such aggressive corrosives as flue dust, fly ash, molten glass, etc. require more oxidation and/or corrosion-resistant materials.
Apart from the above, what is also required for such applications is a material which offers in addition to high strength at operating temperatures, including stress-rupture and tensile characteristics, sufficient fabricability that it can be formed into flat rolled products such as sheet, strip, etc, which product forms can be formed into tubing, rings, canisters and other shapes. Without fabricability the utility of an ODS material is significantly diminished.
Apart from '161 reference also might be made to the work of Kornilov, "Aluminum in Iron and Steel" by S. C. Case and K. R. Van Horn, John Wiley and Sons (1953). Kornilov studied the effect of up to 10% aluminum and up to 65% chromium on scaling losses in both cast and wrought Fe-Cr-Al alloys. Aluminum benefited scaling resistance but seemingly there was little benefit conferred by chromium beyond the 25% level at 1100.degree.-1400.degree. C. Nothing in the Kornilov investigation involved fabricability of an ODS product or manufacture of sheet.
R. Allen and R. Perkins (in a contract report for the Naval Air Systems Command, May 1973) investigated ODS iron-chromium-aluminum-yttrium alloys with 16-25% chromium at an aluminum level of 5.7-6.0% versus conventional wrought and cast 25% Cr/4% Al and 15% Cr/4% Al alloys. It was indicated that such alloys could be extruded but nothing was given in terms of fabricability and the production of, say, the important sheet product form .